CA1104806A - Electrolyte for electrochromic display device - Google Patents
Electrolyte for electrochromic display deviceInfo
- Publication number
- CA1104806A CA1104806A CA314,922A CA314922A CA1104806A CA 1104806 A CA1104806 A CA 1104806A CA 314922 A CA314922 A CA 314922A CA 1104806 A CA1104806 A CA 1104806A
- Authority
- CA
- Canada
- Prior art keywords
- display device
- electrolyte
- anions
- electrochromic display
- phosphite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/15—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on an electrochromic effect
- G02F1/1503—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on an electrochromic effect caused by oxidation-reduction reactions in organic liquid solutions, e.g. viologen solutions
Landscapes
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)
- Devices For Indicating Variable Information By Combining Individual Elements (AREA)
Abstract
Abstract According to the invention either or both hypophosphite or phosphite anions are used in an electrochromic electrolyte. The electrochromic electrolyte according to the present invention exhibits improved erasure time. The use of hypophosphite anions also improves substantially the transition time.
Description
This invention relates to an electrolyte Eor use in an electrochromic display device.
Although various kinds of devices are known as electro~
chromic, for the purposes o~ this specification an electro-chromic display device is that which produces a display e~ect by the electrodeposition of a coloured species from a liquid electrolyte onto a display electrode as a result of a reduction-oxidation reactionO The electrolyte is colourless or tinted in a colour which contrasts with the deposited Species.
- The basis of operation of an electrochomric display device of the kind considered here is the electrochemical and chemical interaction hetween a suitable cation, V , and an anion A . Upon reduction of the cation a stable radical is ~ormed:
V+~ ~ e -~ V~
This combines with the anion to precipitate on the cathode (display electrode) to form a film whose resistance depends on the anion:
V + A ~~ V A
Studies of the electrolyte can proceed in two virtually independent directions. Improvements can be sought in the -cation or in the anion~
Of special interest as cations are the viologens, some ; of which, together with a large number of anions, are de-scribed and claimed in U.S. Patent 3,854,794 issued December 17, 1974 to~Van Dam et al. (German Patent 2,260,048~. In a papex by 5choot C.J.,~Ponjee J. J. et al. 1973 J. Appl. Phys. Vol.
23, p. 64, the particular electrolyte studied was diheptylviolo-gen dibromide (N~W7-di-heptyl, 4,~4'~bipyridinium dibromide).
~30 On reduction of the viologen, a deep blue precipitate is formed with the bromide anion at the display electrode. At :: B ~
- . . ...
- . ~ . ..
.
the anode a reverse reaction occurs. It has been found that the bromide anion corrodes and discolours the metal surface of the display electrode especially when silver, which is a highly preferred metal, is used, and that repeated reduction/
o~idation cycles result in a non-erasible deposit on the cathode due to recrystallization of the radical cation deposit.
In U.S. Patent 3,950,077 issued April 13, 1976 to Raymond J. Jasinski, it is suygested that dihydrogen phosphate radical (E2PO4 ), or bicarbonate radical (HC03 ), be substituted for the bromide anion. The use of dihydrogen phosphate radical has sol~ed the recrystallization and corrosion problems but the speed of the reactions at the electrodes is substantially reduced. In particular, erasure of the precipitate, hesides being very slo~, has been found to be highly temperature sensitive in the range of normal ambient temperaturesl the erasure time increasing as temperature falls. Bicarbonate radical is not preferred by Jasinski.
It has been found th~t the precipitate formed with di-hydrogen phosphate radical is highly resistive due, it is thought to the unpolarizable nature of the dihydrogen phosphate molecule.
~ asinski, in his paper "The Electrochemistry of Some n-Heptylviologen Salt Solutions" published in the Journal of the Electrochemical Society, May 1977, p. 637-640, considers besides H2PO4 and HCO3 , several other anions including So~2 , F , formate radical (HCOO ~, and acetate radical (CH3COO ~.
U.S. Patent 3,712,709 issued January 23, 1973 to Kenworthy proposes as cations N(p-cyanophenol) substituted derivatives of a compound having two conjugated nitrogen containing aromatic rings, and as anions chloride and ferrocyanide.
Although various kinds of devices are known as electro~
chromic, for the purposes o~ this specification an electro-chromic display device is that which produces a display e~ect by the electrodeposition of a coloured species from a liquid electrolyte onto a display electrode as a result of a reduction-oxidation reactionO The electrolyte is colourless or tinted in a colour which contrasts with the deposited Species.
- The basis of operation of an electrochomric display device of the kind considered here is the electrochemical and chemical interaction hetween a suitable cation, V , and an anion A . Upon reduction of the cation a stable radical is ~ormed:
V+~ ~ e -~ V~
This combines with the anion to precipitate on the cathode (display electrode) to form a film whose resistance depends on the anion:
V + A ~~ V A
Studies of the electrolyte can proceed in two virtually independent directions. Improvements can be sought in the -cation or in the anion~
Of special interest as cations are the viologens, some ; of which, together with a large number of anions, are de-scribed and claimed in U.S. Patent 3,854,794 issued December 17, 1974 to~Van Dam et al. (German Patent 2,260,048~. In a papex by 5choot C.J.,~Ponjee J. J. et al. 1973 J. Appl. Phys. Vol.
23, p. 64, the particular electrolyte studied was diheptylviolo-gen dibromide (N~W7-di-heptyl, 4,~4'~bipyridinium dibromide).
~30 On reduction of the viologen, a deep blue precipitate is formed with the bromide anion at the display electrode. At :: B ~
- . . ...
- . ~ . ..
.
the anode a reverse reaction occurs. It has been found that the bromide anion corrodes and discolours the metal surface of the display electrode especially when silver, which is a highly preferred metal, is used, and that repeated reduction/
o~idation cycles result in a non-erasible deposit on the cathode due to recrystallization of the radical cation deposit.
In U.S. Patent 3,950,077 issued April 13, 1976 to Raymond J. Jasinski, it is suygested that dihydrogen phosphate radical (E2PO4 ), or bicarbonate radical (HC03 ), be substituted for the bromide anion. The use of dihydrogen phosphate radical has sol~ed the recrystallization and corrosion problems but the speed of the reactions at the electrodes is substantially reduced. In particular, erasure of the precipitate, hesides being very slo~, has been found to be highly temperature sensitive in the range of normal ambient temperaturesl the erasure time increasing as temperature falls. Bicarbonate radical is not preferred by Jasinski.
It has been found th~t the precipitate formed with di-hydrogen phosphate radical is highly resistive due, it is thought to the unpolarizable nature of the dihydrogen phosphate molecule.
~ asinski, in his paper "The Electrochemistry of Some n-Heptylviologen Salt Solutions" published in the Journal of the Electrochemical Society, May 1977, p. 637-640, considers besides H2PO4 and HCO3 , several other anions including So~2 , F , formate radical (HCOO ~, and acetate radical (CH3COO ~.
U.S. Patent 3,712,709 issued January 23, 1973 to Kenworthy proposes as cations N(p-cyanophenol) substituted derivatives of a compound having two conjugated nitrogen containing aromatic rings, and as anions chloride and ferrocyanide.
- 2 -,~
.~
In papers delivered at -the Fall Meeting of the Electro-chemical Society~ OCtober 17-22, 1976 at Las Vegas J. ~. Ponjee and J. Bruinink propose the use of a new viologen cation -tetramethyl bis - 4(1-benzyl pyridin-4'-yl) pyridinium - with a large anion such as BF4 or CIO4 . These electrolytes seem to require a SnO2 electrode.
According to the in~ention either or both hypophos-phite or phosphite anions are used in an electrochromic electrolyte.
Hypophosphite radical (H2PO2 ) and phosphite radical tH~032 ) can be characterized as the oxo anions containing one phosphorus atom and with phosphorus oxiclation states lower than orthophosphate radical (PO43 ).
Phosphite and~or hypophosphite anions can be used either aloneor buffered with dihydrogen phosphate anions and/or with bromide anions. ~lthough studles ha~e confirmed the improved performance of phosphite and hypophosphite anions : with heptyl viologen, the results extend to ~iologens with other side chains and multiple bipyridinium structures. The invention is appl;cable to any of the cations referred to in the discussion above.
Although aqueous electrolyte solutions are genexally pre-ferred, some cations require organic solvents~ The invention comprises both fo~ms of solvent.
In one aspect of th;s inventIon, there is provided for use in an elect:rocho~ric display device, a display electrode, an anode, and an aqueous electrolyte solut;on disposed there-between whl`ch produces a display effect by electrodeposition of a colored species from the electrolyte onto the display electrode as a result of a redox reaction, the improvement according to ~hich the electrolyte comprises an anion which is either hypophosphite or phosphite and a cation which has
.~
In papers delivered at -the Fall Meeting of the Electro-chemical Society~ OCtober 17-22, 1976 at Las Vegas J. ~. Ponjee and J. Bruinink propose the use of a new viologen cation -tetramethyl bis - 4(1-benzyl pyridin-4'-yl) pyridinium - with a large anion such as BF4 or CIO4 . These electrolytes seem to require a SnO2 electrode.
According to the in~ention either or both hypophos-phite or phosphite anions are used in an electrochromic electrolyte.
Hypophosphite radical (H2PO2 ) and phosphite radical tH~032 ) can be characterized as the oxo anions containing one phosphorus atom and with phosphorus oxiclation states lower than orthophosphate radical (PO43 ).
Phosphite and~or hypophosphite anions can be used either aloneor buffered with dihydrogen phosphate anions and/or with bromide anions. ~lthough studles ha~e confirmed the improved performance of phosphite and hypophosphite anions : with heptyl viologen, the results extend to ~iologens with other side chains and multiple bipyridinium structures. The invention is appl;cable to any of the cations referred to in the discussion above.
Although aqueous electrolyte solutions are genexally pre-ferred, some cations require organic solvents~ The invention comprises both fo~ms of solvent.
In one aspect of th;s inventIon, there is provided for use in an elect:rocho~ric display device, a display electrode, an anode, and an aqueous electrolyte solut;on disposed there-between whl`ch produces a display effect by electrodeposition of a colored species from the electrolyte onto the display electrode as a result of a redox reaction, the improvement according to ~hich the electrolyte comprises an anion which is either hypophosphite or phosphite and a cation which has
3 -a bipyridinlum s-tructure.
By way of example, the following table gives the take-off or transition times for different current densities and the erase ; :;
:; :
' :
- 3a -.........
times for heptyl viologen with dihydr~gen phosphate radical as the anion Ccolumn i), with ~oth phosphite and dihydrogen phosphate radicals as anions ~column II), and with both hypo-phosphite and dihydrogen phosphate radicals as anions (column III).
The transition time is the time after which, for a given current density and electrochromic material concentration, undesirable electrochemical reactions occur, and is a measure of the diffusion coefficient or of the resiOEtivity of the precipitate.
A long transition time is advantageous in an electrochromic display slnce it enables more material to be pre~ipitated at a single operation. This i8 important in speedily achieving the required a~ount of precipitate in a display device with many disp~ay electrodes. The initial solution was O.lM heptyl viologen d~hydrcgen phosphate in lN phosphate buffer. pH of the solution was 5.6. The temperature at which the measurements were made was 25@C. The phosphite and hypophosphite anions were obtained by saturating the initial solution with sodium phosphite and sodium hypophosphite respectively. The cathode was a plated silver electrode.
TABLE
Current Density Transition Time (ms.~
mA/cm2 I II III
130 4.5 5.0 28 260 2.0 1.5 10 Erase Time (ms.) ~ 450 45 45 It will be noted that for the particular proportions of the experiment, the use of phosphite anions did not improve transition times whereas hypophosphite anions, besides showing the improved erasure time of phosphlte, sub9tantially improved the transi~ion time.
By way of example, the following table gives the take-off or transition times for different current densities and the erase ; :;
:; :
' :
- 3a -.........
times for heptyl viologen with dihydr~gen phosphate radical as the anion Ccolumn i), with ~oth phosphite and dihydrogen phosphate radicals as anions ~column II), and with both hypo-phosphite and dihydrogen phosphate radicals as anions (column III).
The transition time is the time after which, for a given current density and electrochromic material concentration, undesirable electrochemical reactions occur, and is a measure of the diffusion coefficient or of the resiOEtivity of the precipitate.
A long transition time is advantageous in an electrochromic display slnce it enables more material to be pre~ipitated at a single operation. This i8 important in speedily achieving the required a~ount of precipitate in a display device with many disp~ay electrodes. The initial solution was O.lM heptyl viologen d~hydrcgen phosphate in lN phosphate buffer. pH of the solution was 5.6. The temperature at which the measurements were made was 25@C. The phosphite and hypophosphite anions were obtained by saturating the initial solution with sodium phosphite and sodium hypophosphite respectively. The cathode was a plated silver electrode.
TABLE
Current Density Transition Time (ms.~
mA/cm2 I II III
130 4.5 5.0 28 260 2.0 1.5 10 Erase Time (ms.) ~ 450 45 45 It will be noted that for the particular proportions of the experiment, the use of phosphite anions did not improve transition times whereas hypophosphite anions, besides showing the improved erasure time of phosphlte, sub9tantially improved the transi~ion time.
- 4 -,~,,~ , ' ~, .. . .. .
3~
E~cess of the anipnic .species oyer the yiologen dlcation is desirable for reas~ns of pr~ci!~itat~ stability and con-ductivlty and is achieved by adding the required anions as a sodium or potassium salt.
Besides the electrochromic display devices described ln the above-referred to British Patent Specification 1,376,799 and U.S. Patent 3,950,077, a different orm of electrochromlc display device - a matrix addressed display - suitable for use with the electrolyte of the invention is described in our commonly assigned copending Canadian application 268.,797, filed December 29, 1976 and entitled I~Method of Operating an Electrochromic Display Device".
.
3~
E~cess of the anipnic .species oyer the yiologen dlcation is desirable for reas~ns of pr~ci!~itat~ stability and con-ductivlty and is achieved by adding the required anions as a sodium or potassium salt.
Besides the electrochromic display devices described ln the above-referred to British Patent Specification 1,376,799 and U.S. Patent 3,950,077, a different orm of electrochromlc display device - a matrix addressed display - suitable for use with the electrolyte of the invention is described in our commonly assigned copending Canadian application 268.,797, filed December 29, 1976 and entitled I~Method of Operating an Electrochromic Display Device".
.
- 5 -~ .. ..
Claims (7)
1. In an electrochromic display device which com-prises a display electrode, an anode, and an aqueous electrolyte solution disposed therebetween which produces a display effect by electrodeposition of a colored species from the electrolyte onto the display electrode as a result of a redox reaction, the improvement according to which the electrolyte comprises an anion which is either hypophosphite or phosphite and a cation which has a bipyridinium structure.
2. An electrochromic display device as claimed in claim 1 wherein the electrolyte comprises hypophosphite anions.
3. An electrochromic display device as claimed in claim 1 wherein the electrolyte comprises phosphite anions.
4. An electrochromic display device as claimed in claim 1 wherein the electrolyte comprises both hypophosphite anions and phosphite anions.
5. An electrochromic display device as claimed in claim 1 wherein the electrolyte also includes bromide anions.
6. An electrochromic display device as claimed in claim 1 wherein the electrolyte also includes dihydrogen phosphate anions.
7. An electrochromic display device as claimed in claim 1 wherein the electrolyte comprises heptyl viologen cations.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4550077 | 1977-11-02 | ||
| GB45500 | 1977-11-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104806A true CA1104806A (en) | 1981-07-14 |
Family
ID=10437458
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA314,922A Expired CA1104806A (en) | 1977-11-02 | 1978-10-30 | Electrolyte for electrochromic display device |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4187003A (en) |
| EP (1) | EP0001912B1 (en) |
| JP (1) | JPS6017360B2 (en) |
| CA (1) | CA1104806A (en) |
| DE (1) | DE2860285D1 (en) |
| IT (1) | IT1160027B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55106282A (en) * | 1978-11-25 | 1980-08-14 | Matsushita Electric Ind Co Ltd | Electrochromic display device |
| US4402573A (en) * | 1981-06-18 | 1983-09-06 | International Business Machines Corporation | Materials for electrochromic display devices |
| EP0069174B1 (en) * | 1981-06-30 | 1987-03-04 | International Business Machines Corporation | Method and electrolytic display for selectively displaying an image |
| FR2516680A1 (en) * | 1981-11-16 | 1983-05-20 | Anizan Paul | Electrolytic display cell contg. phenothiazine derivs. - with two oxidn. states of differing colour |
| EP0083668B1 (en) * | 1981-12-24 | 1986-08-20 | International Business Machines Corporation | Electrolytic display device employing metal ion catalysis |
| JPS61107323A (en) * | 1984-10-31 | 1986-05-26 | Sony Corp | Elecrtochromic display apparatus |
| JPS6339686A (en) * | 1986-08-06 | 1988-02-20 | Nippon Kokan Kk <Nkk> | Method for treating seawater |
| US5780160A (en) * | 1994-10-26 | 1998-07-14 | Donnelly Corporation | Electrochromic devices with improved processability and methods of preparing the same |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3951521A (en) * | 1964-06-02 | 1976-04-20 | Xerox Corporation | Reversible radiant energy filter and process of using same |
| US3451741A (en) * | 1966-06-15 | 1969-06-24 | Du Pont | Electrochromic device |
| US3774988A (en) * | 1969-09-02 | 1973-11-27 | Polaroid Corp | Variable light-filtering device |
| NL166053C (en) * | 1970-06-27 | 1981-06-15 | Philips Nv | IMAGE DISPLAY DEVICE. |
| US3712709A (en) * | 1971-11-22 | 1973-01-23 | Ici Ltd | Variable light transmission device |
| BE793156A (en) * | 1971-12-23 | 1973-06-21 | Philips Nv | IMAGE REPRODUCING CELL |
| NL167774C (en) * | 1973-05-04 | 1982-01-18 | Philips Nv | IMAGE DISPLAY CELL, AND METHOD FOR PREPARING COMPOUNDS, WHICH CAN BE USED IN THIS IMAGE DISPLAY CELL. |
| GB1506560A (en) * | 1974-03-15 | 1978-04-05 | Ici Ltd | Device |
| US3961842A (en) * | 1974-09-20 | 1976-06-08 | Texas Instruments Incorporated | Regenerating electrode for electrochromic display cell |
| US3950077A (en) * | 1974-09-20 | 1976-04-13 | Texas Instruments Incorporated | Lead reference and counter electrode for an electrochromic display |
| US4116535A (en) * | 1976-05-10 | 1978-09-26 | U.S. Philips Corporation | Picture display cell with memory effect |
-
1978
- 1978-08-21 US US05/935,399 patent/US4187003A/en not_active Expired - Lifetime
- 1978-10-30 CA CA314,922A patent/CA1104806A/en not_active Expired
- 1978-10-30 EP EP78300562A patent/EP0001912B1/en not_active Expired
- 1978-10-30 DE DE7878300562T patent/DE2860285D1/en not_active Expired
- 1978-10-31 IT IT29279/78A patent/IT1160027B/en active
- 1978-11-02 JP JP53134633A patent/JPS6017360B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5474288A (en) | 1979-06-14 |
| DE2860285D1 (en) | 1981-02-05 |
| EP0001912B1 (en) | 1980-11-12 |
| IT7829279A0 (en) | 1978-10-31 |
| US4187003A (en) | 1980-02-05 |
| IT1160027B (en) | 1987-03-04 |
| EP0001912A1 (en) | 1979-05-16 |
| JPS6017360B2 (en) | 1985-05-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |